The present invention relates to spinal column spacers.
The human spinal column consists of 33 (sometimes 34) vertebrae divided into five groups: cervical, thoracic, lumbar, sacral and coccygeal vertebrae areas. The sacral vertebrae are fused into a single bone as is the coccygeal vertebrae, usually designated as the coccyx. The movable vertebrae are found in the cervical, thoracic and lumbar areas. Each area has a characteristic curve. Thus, various vertebrae differ in size and shape depending on their location in the spinal column.
Spacers exist for repairing the spinal column. Most of the known spacers are designed for the lumbar or thoracic regions of the spine. Since the lumbar or thoracic vertebrae are structurally different from the cervical vertebrae, spacers designed for the lumbar or thoracic region will not perform properly in the cervical region. Most devices used clinically for repairing the anterior cervical area of the spine usually involve some elements of screw, plate, and spacers for bony attachment and/or support.
Various prior art cervical spacers are known. These devices may be made from X-ray transparent materials or from X-ray opaque materials. Devices made from X-ray transparent materials typically are, as the name implies, difficult to see on routine radiographic X-ray studies. Although they may be visualized on expensive CT scans with a much high patient radiation dose, these spacers still cannot be seen directly on plain radiographic images that are routinely used for follow up examination and monitoring of the bony healing and alignment. It has been proposed to solve this imaging problem by adding dots or spots of X-ray opaque markers to the spacers. However the position of the spacer must be inferred on the basis of these markers, generally leaving some ambiguity of the exact position of all of the edges. Devices made from X-ray opaque materials, on the other hand, can be seen on X-ray, but the opaqueness often makes it difficult to assess the status of healing grafting material inside the spacer, and in some cases difficult to assess the position of the attaching screws of the construct. One method directed to solving this problem is a skeletal frame that is opaque to X-rays, but, because of being a skeletal structure, has openings that allow X-ray passage and therefore permit the doctor to view the interior of the spacer. Specifically, these spacers employ a skeletal frame of a material such as titanium, the skeletal form providing multiple openings allowing X-ray visualization of the interior of the spacer. Regarding the known designs for cervical spacers, these represent the state of the art that strives to meet two important performance criteria: strength, increased by the titanium frame, and X-ray transparency, provided by the multiple openings of the skeletal frame.
The present inventors have identified, however, that this state-of-the-art cervical spacer, constructed with a skeletal form, regardless of the specific shape of the skeletal form, must arrange and dimension the skeletal member to proved windows or openings large enough to enable viewing of the interior of the skeletal form by X-ray. These windows allow the doctor to monitor the process of as the surgical arthrodesis heals to a mature fusion between the upper and lower vertebrae. However, it is inherent to a skeletal structure cervical spacer that these windows or openings cannot be enlarged formed without sacrificing strength of the device. Simply put, to make the openings larger there are two options: make the skeletal members with a smaller diameter, or use fewer skeletal members. Both of these decrease strength
Various embodiments of the disclosed invention solve these long-felt needs for practical stabilization of the cervical vertebrae and offer additional features and benefits, such as, for example, significantly increased strength to the spacer while maintaining sufficient X-ray transparency or translucency to enable proper follow-up monitoring with conventional X-ray methods.